HIV prevention programs have been successful in reducing HIV transmission behaviors for both HIV seronegative and seropositive persons. Despite the demonstration that particular intervention strategies can be successful in changing targeted risk behaviors, gains have not been maintained equally for all, and furthermore, the overall national incidence of HIV has not been declined. Health disparities are endemic to those at-risk and infected with HIV in Los Angeles Country and nationally; African American and Latino men and women are proportionately 3 times more likely to acquire HIV than Caucasians and HIV infection rates in these groups are increasing. More than three million immigrants from nearly 100 countries living in L.A. County are an emerging risk group. With the substantial ethnic/racial disparities in infection rates nationally and in L.A., it is critical to develop effective interventions for these populations. Intervention science also faces a great challenge. There is a large gap between the type and scope of interventions demonstrated at efficacious and providers' practices in community-based agencies and service settings. This gap, widened further by the geographic, cultural, and resource differences existing in L.A. county, provides a great opportunity for the Intervention Core to address CHIPTS' goals utilizing a virtual community inclusive of local academicians, policymakers, community-based agencies, and activists. Such a virtual community enables development of a multiple intervention research agenda that exploits Internet-based and electronic technologies. Development of a virtual community also facilitates methods for reducing gaps in technical knowledge between agencies and academics, in communication between providers and consumers of prevention services, and in the speed and access of high-quality, information for participants in the community. This Intervention Core, which is a new Core to CHIPTS, reflects the overall mission of the Center by implementing the participatory action model in all its activities. The Intervention Core is distinguished from Treatment services by focusing on interventions for individuals, small groups, and communities. (Treatment services focuses on providers, community-based agencies, and systems-of-care.) In addition, the Core supports development and refinement of the science of intervention and evaluation and offer opportunities for introducing new technologies in dissemination. Over the next five years, CHIPTS Intervention Core will provide infrastructure support to advise and to shape traditional intervention approaches (including those that sustain risk reduction changes), while also encouraging and facilitating innovative intervention research programs that move beyond traditional methods (e.g., using the Internet) when working with the highest risk populations (immigrants and those with comorbid disorders) and the infected.